The present invention relates generally to a steel strip heating furnace for heating steel strips conveyed along a preset course. More particularly, the invention relates to a steel strip heating furnace which can eliminate the adverse influence of heat radiation.
The structure of a typical furnace 10 is shown in FIG. 1 in transverse section. The furnace 10 has a furnace body comprising a ceiling 12, a floor 14 and side walls 16 extending between the ceiling and the floor. The course for the steel strips 20 is defined within the furnace body by a skid beam 22 supported on the floor 14. A plurality of the steel strips 20 are mounted on the skid beam 22 transversely across the course, and forcibly transported along the course.
As they travel along the course, the steel strips 20 are heated by radiation from the furnace body. Therefore, the central section 20A of each steel strip 20 generally receives heat radiated by the ceiling 12 and the floor 14. On the other hand, the ends 20B of the steel strips are subject not only to heat from the ceiling 12 and floor 14 but also from the opposing side wall 16. Therefore, the end sections 20B receive more heat than the central section. This generates a thermal gradient between the central section 20A and the end sections 20B, and, as a result tends to heat the end sections 20B excessively. These thermal gradients generate deformation stresses between the end sections and the central section.
In view of the above defect, an improvement to this furnace, shown in FIG. 2 has been proposed. In the proposed improvement, an attempt has been made to reduce the effective heat radiation area by forming a recess in the side wall of the furnace opposite the transverse edges of the steel strip. The recess 18 is of depth ab (=cd) and width (bc) which are significantly smaller than the depth AB(=CD) and width (BC) of the corresponding area of the furnace of FIG. 1. Since the heating at the transverse ends of the steel strip is determined by effective heat radiation area (ab.times.bc.times.furnace length), the end heating can be moderated by reducing the effective heat radiation area (AB.times.BC.times.furnace length) of the furnace of FIG. 1.
However, even the improvement of FIG. 2 is not fully satisfactory in that it does not actually control the heat radiation applied to the transverse ends of the steel strip, but rather relies solely on geometry for even heating.